Electric heating unit for clothes dryers

ABSTRACT

A heater box assembly for an electrically heated clothes dryer has a pair of spaced insulators with a wire heating element wound around the two insulators and with adjacent turns spaced apart. The support for the heating unit includes at least one spring acting on at least one insulator to apply a tension on the wire heating element to compensate for the change in length of the wire element due to thermal expansion. The box-like support is snugly received in a flanged opening of a wall of the dryer to form the heated air inlet for the dryer and mounting means including one or more tabs on the box for insertion into one or more corresponding slots in the flanged opening and a single fastener for securing the box at a side removed from the position of the slot or slots.

United States Patent 1 91 Zenz 1 ELECTRIC HEATING UNIT FOR CLOTHES DRYERS [75] Inventor: Fred J. Zenz, Berrien Springs, Mich.

[731 Assignee: Whirlpool Corporation, Bonton Harbor, Mich.

221 Filed: Nov. 18,1971

1211 App1.No.:199,994

Related US. Application Data [62] Division of Ser. No. 29,388, April 17, 1970, Pat. No.

[ Mar. 26, 1974 2,806,475 9/1947 Smillie 206/195 F X Primary ExaminerGe0rge E. Lowrance Assistant Examiner-Stephen Marcus Attorney, Agent, or FirmHil1, Sherman, Meroni, Gross & Simpson [57] ABSTRACT A heater box assembly for an electrically heated clothes dryer has a pair of spaced insulators with a wire heating element wound around the two insulators and with adjacent turns spaced apart. The support for the heating unit includes at least one spring acting on at least one insulator to apply a tension on the wire heating element to compensate for the change in length of the wire element due to thermal expansion. The box-like support is snugly received in a flanged opening of a wall of the dryer to form the heated air inlet for the dryer and mounting means including one or more tabs on the box for insertion into one or more corresponding slots in the flanged opening and a single fastener for securing the box at a side removed from the position of the slot or slots.

2 Claims, 12 Drawing Figures minimums m4 31799887 sum 3 er 5 PATENIEDIARZB m4 3.799.387

saw or 5 PAIENIEllmas am 3799387 sum 5 m 5 JEJ H which cause premature failure.

ELECTRIC HEATING UNIT FOR CLOTHES DRYERS i This is a division of application Ser. No. 29,388 filed Apr. 17, 1970 which application issued on June l3, 19.72 as U.S. Pat. No. 3,670,143.

BACKGROUND OF THE INVENTION v heating unit has the disadvantage of being expensive to manufacture and expensive to install it in an appliance such as a dryer. Many of the heating units used in dryers are disposed with the length of the wire of the heating unit running substantially parallel or at a slight angle to the direction of the air flow so that various sections of the heating element are in contact with air of different temperatures andthe unit develops hot spots SUMMARY or THE INVENTION The present invention provides a heater'box assembly ofa box having means of mounting a heating unit therein. Preferably theheating unit comprises a wire ,elementwound between a pair of spaced insulators and mounting means, which biases the insulator apart to compensate for thermal expansion, positioning the heating wire with the wire element extending transverse to the air flow to-prevent unequal cooling of the wire element. In the preferred embodiment the box is formed 'in. sections which when secured together provide the mounting means for holding one of the insulators in a substantially rigid position and the other insulator being free for relative movement thereto. The mounting meansinclude springs disposed on the outside. of the box for biasing the other insulator away from the one insulator. The present invention also provides an expedient manner for attaching the heater box assembly to an appliance utilizing one or more coacting tabs and slots and a single retaining means.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a rear view of a clothes dryer with portions broken away'for purposes of illustration showing the heater box assembly of the present invention mounted FIG. 5, which is located on the sheet with FIG. 1, is an enlarged view of a resilient mounting means used in the'heater box assembly of FIGS. 3 and 4;

FIG. 6 is an enlarged cross-sectional view of a tab and slot arrangement illustrated in the circle identified by VI in FIG. 4;

FIG. 7 is a view similar to FIG. 3 of an embodiment of the heater box assembly of the present invention;

FIG. 8 is a cross-sectional view taken along lines VIII- -VIII of FIG. 7;

FIG. 9 is a view similar to FIG. 3 of a third embodiment of a heater box assembly of the present invention;

FIG. 10 is a cross-sectional view taken along lines XIXI of FIG. 10;

FIG. 11, which is located on the sheet with FIG. I, is a cross-sectional view of an embodiment of an insulator of the present invention; and

FIG. 12 is a side view of the insulator of FIG. 11 with portions removed for purposes of illustration.

DESCRIPTION OF THE PREFERRED EMBODIMENT Although the principles of the present invention can be utilized in a heater box assembly for any apparatus, they are particularly useful in a heater box assembly generally indicated at 15 attached to a laundry device suchas an electrically heated dryer generally indicated at 16 in FIG. 1. The electrically heated dryer 16 has an outer casing 17 made of a back panel 18, a pair of side panels 19, 20 and a front panel not illustrated. Extending between the side panels 19 and 20 and extending parallel to the back panel 18 is a wall or bulkhead 21, which, as best illustrated in FIG. 2 has an annular beaded embossment 22 formed thereon to receive a sealing means attached to the rear end of a rotatable dryer drum (not shown). The bulkhead 21 is provided with an exhaust or outlet opening 23 which is covered by a grill and an oval opening 24 having a peripheral flange 25 defining an inlet opening for a heating chamber defined by thefront surface of the bulkhead and the rotatable drum. The heater box assembly 15 is mounted on the bulkhead 21 at the opening 24 to heat air entering the drying chamber. Disposed on the rear side or surface of the bulkhead 21 is an air duct 26 (FIG. 1) in communication with the exhaust opening 23 and extending to a blower housing 27 which has an exhaust outlet 28. During the drying operation a blower mounted in the blower mounting 27 creates a suction causing air to enter the drying chamber by passing through the heater box 15 through the inlet opening 24 following the path of the arrows through the heating chamber to be withdrawn through the exhaust opening 23. After leaving the heating chamber through the exhaust opening 23, the air is pulled through the duct 26 to the blower housing 27 and expelled through the exhaust outlet 28 of the blower housing. An example of a laundry dryer and a description of its complete struc ture and operation is set forth in U. S. Pat. No. 3,398,465 which is assigned to the assignee of this application.

Referring to FIGS. 3 and 4, the heater box assembly 15 is made up of a pair of metal members 30 and 31 each of which has deformed portions so that when the two members are attached together they define a heating chamber 32. Both'the members 30 and 31 are preferably formed of sheet metal by a metal stamping process which provides a peripheral edge or flange 33 and 34 respectively, which are used for securing the two members together in a conventional manner such as by fastening means 35.

The member 30, which has a dished or concave portion 36, has a series of parallel louvers 37 extending across the bottom of portion 36, which louvers define inlet means for admitting air into the chamber 32. The member 30 is also provided with an aperture 38 for receiving a temperature sensing means such as a thermostatic control of a conventional design.

The member 31 has a depressed portion of a cup shape with a bottom 40 which has been further shaped to provide a projecting portion 41 with a reversely bulged or indented bottom 42 which is provided with a pattern of perforations 43 to define an air inlet for the drying chamber of dryer 16. The projecting portion 41 has side walls 44 and has an oval configuration complementary to the opening 24 in the bulkhead 21. The size of the projecting portion 41 is selected so that the side walls 44 are received in the peripheral flange 25 in a snug engagement.

As best illustrated in FIG. 6, the side wall 44 is provided with a bend 45 which abuts against an edge 46 of the peripheral flange 25 to limit insertion of the portion 41 into opening 24. The side wall 44 is also provided with a tab 47 which is inserted into slot 48 formed in the peripheral flange 25. The slot 48 and the tab 47 coact as shown in FIGS. 4 and 6, to attach the lower end of the projecting portion 41 to the peripheral flange 25 of the bulkhead 21.

To complete the mounting or attachment of the heater box assembly in the opening 24, a retaining means generally indicated at 50 (FIG. 3) comprising a strap 51 which is attached at one end to the member 31 and at the other end carries a fastening means such as a screw 52 for securing the strap to the bulkhead 21. Thus, by engagement of the coacting slot 47 and tab 48 and the single fastening means of the retainer 50, the box assembly 15 is secured in the opening 24. It is to be realized that the coacting tab or tabs and slot or slots can be at other locations on the side wall 44 such as one side. The retaining means 50 would be mounted opposite to the coating tab and slot retainer regardless of which portion of side wall 44 is utilized.

Disposed in the chamber 32 of the heater box assembly 15 is a heating unit generally indicated at 53 including a pair of spaced elongated or bar insulators 54 and 55 and a wire heating element 56 which is wound or looped around the pair of insulators 54 and 55 to provide wire loops or turns 57. Adjacent turns are spaced apart by axial spaced fins 58 on each of the insulators 54 and 55. To anchor the wire heating element, the end turns 59 are passed by the upper insulator 54 on the opposite side relative to the other turns 57 to form the cross wire configuration illustrated in FIG. 4. Each of the ends of the element 56 are then passed through the box assembly 15 by extending through a hollow insulator 60 and is then connected to a source of electrical energy. Alternately, terminals may be welded or crimped to the ends of element 56 with said terminals being retained by the hollow insulators 60.

To mount the insulators 54 and 55 of the heating unit 53 the members 30 and 31 are provided with coacting mounting means which receive end portion 61 of the insulators 54 and 55, which end portions 61 have a re- 7 duced diameter and a circumferential groove 62. As

illustrated, each of the members 30 and 31 are provided with a pair of aligned semicircular cutout portions on the peripheral edge to form a pair of circular apertures or openings 63 to receive each of the end portions 61 of the upper insulator 54 which end portions protrude from the heater box assembly 15. The openings 63 maintain the upper insulator 54 in a substantially fixed position with respect to the heater box assembly 15. The lower insulator 55 has its reduced end portion 61 protruding from the heating chamber 32 and being received in elongated cutout portions 65 and 66 formed respectively in the members 30 and 31 which cutout portions 65 and 66 form an elongated aperture enabling relative movement of the insulator 55 when mounted.

The flanges 33 and 34 have portions removed at the respective cutout portions to provide clearance for the end portions 61 of the insulators. It should be realized that insulators 54 and 55 could be provided with rectangular end portions rather than reduced diameter portions 61. In the event that rectangular end portions be provided, the members 30 and 31 would be provided with appropriately dimensioned cutouts to receive the modified insulators.

To compensate for thermal expansion in the wire heating element 56, while in use, bearing means such as a pair of springs 69 are provided to maintain a tensioning force on the loops 57 of the wire element 56 by urging the lower insulator 55 away from the upper insulater 54. As best illustrated in FIGS. 3 and 5, each of the springs 69 has an end 70 received by a notch on the exterior of the heater box assembly 15 and the other end has a hook or loop 71 which is received in the groove 62 of the end portion 61.

In operation, air drawn into the dryer chamber by the blower in the blower housing 27, is drawn through the louvers 37, which forms the inlet means of the heater box assembly 15, into the chamber 32. As the air moves across the loops 57 of the wire heating element, it is heated and then passes through the perforations 43 into the dryer chamber of the dryer 16. Since a tensioning force is applied to the loops 57 of the wire element 56 by the springs 69 pulling the lower insulator 55 away from the upper insulator, any slack in the loop 57 of the wire element 56, which slack is the result of a change in length due to thermal expansion, is removed by the tension applied by the springs 69. By placing the springs on the exterior of the box assembly 15, the deleterious effect of the heat emitted by the heating element 56 on the spring characteristics is minimized.

In FIGS. 8 and 9, an embodiment of the heater box assembly is generally indicated at 15a which comprises a pair of members 300 and 31a attached together to define a box means having a heater chamber 32a. Members 300 and 310 are substantially similar to the corresponding members 30 and 31 of the previously described embodiment except they do not have cutout portions on their peripheral edges for providing support means for mounting the insulators of a heating unit.

Disposed in the chamber 32a is a heating unit 53a which comprises an upper insulator 54a and a lower insulator 55a which are substantially similar to the previously described insulators except their length is such that the reduced end portions 61a are disposed in the chamber 32a. As in the previously described heating unit 53, a wire heating element 54a is wound between the two spaced insulators 54a and 55a with turns or loops 57a which are spaced apart by fins 58a on each of the pair of insulators. The primary difference in the structure of the'heater box assembly 15a over the previously described embodiment is the mounting means for mounting the heating unit 53a in the chamber 32a. The mounting means comprises a pair of resilient members 74 which are attached by fastening means 75 to one of the members 30a or 31a and asillustrated to the member 300. The resilient members 74 are provided with eye means 76 at each end to engage a groove 62a formed in each of the reduced end portions 61a. The members 74 are of a spring character so that they bias both the insulators 54a and 55a apart to maintain the desired tension on the loops 57a of the wire heating element 56a.

As in the previously described embodiment, air enters through the louvers 37a formed in the member 30a and flows substantially perpendicular to the plane formed by the wire loops 57 across the heater element 56a and then passes through the perforated bottom 42a of the projecting portion of the member 31a into the drying chamber formed by the bulkhead 21 and the tumbling drum of the laundry .dryer 16.

A third embodiment of the heater box assembly is generally indicated at 15b and illustrated in FIGS. and 11. The heater box assembly b is made up of a pair of members 30b and 31b which are interconnected at the peripheral edge in a manner similar to the previously described embodiments to form a box structure having a heater chamber 32b. The member 30b is provided with louvers 37b to admit air into the heating chamber 32b and the member 31b is provided with a projecting portion 41b having a perforated indented 'bottom 42b which is complementary in shape and size to be snugly received in a peripheral flange of the opening 24 of the bulkhead 21. As in the previously described embodiment of FIGS. 8 and 9, a heating unit generally indicated at 53b comprising an upper cylindrical insulator 54b and a lower cylindrical insulator 55b with the wire heatingelement 54b wound into turns or loops 57b thereon and between. As in the embodiment of FIGS. 8 and 9, the insulators 54b and 55b are of a length so that they are completely contained within the heating chamber 32b.

To mount the heating unit 53b in the chamber 32b, two pairs of brackets 80,80, 81,81, respectively, are attached to one of the members and as illustrated attached to the member b. Each of the brackets 80 has a slot 82 opening in the upward direction towards a top of the heater box assembly 15b. The lower pair of brackets 81 have a slot 83 opening in a direction opposite to the slot 82 and opening at a direction towards the bottom of the heater box 15b. As illustrated, the upper insulating 54b is supported in the pair of brackets 80 with ,its reduced end portions 61b received in the slots 82. The lower insulator 55b has reduced end portions 61b which are received in the slots 83. The reduced endportions 61b of both insulators 54b and 55b are provided with grooves 62b which prevent. axial shifting of the insulators in the brackets.

To bias the pair of insulators 54b and 55b away from each other, a resilient spring 86 is anchored to an eye 87 attached to the interior of the chamber 32b and as is illustrated is attached to a lower wall 88 of the member 30b. The other end 89 of the resilient spring 86 is attached to a wire loop 90 which is received in a groove 91 formed at the center of the insulator 55b. The spring means 86 applies a tension to the loops 57b to maintain the upper insulator 54b in abutting relation with the bottom of the slots 82 and to maintain a desired tension on the wire element 56b to compensate for the expansion during heating of the heating unit.

In each embodiment, the heating unit 53, 53a or 53b can be formed by winding the wire element around the two spaced insulators. Then the unit is installed in the box structure with a minimum amount of labor. It is contemplated that a disposable spacer can be utilized to hold the two insulators such as 54 and 55 the desired distance apart to prevent any entanglement of the wire loops of the heating element. In the embodiments of FIGS. 10 and 11 one pair of brackets which can be the brackets or the brackets 81 will need to be assembled onto the member 30b after the other pair has received its respective insulator.

In each of the embodiments the air enters the louvers on the member 30, 30a or- 30b and passes in a direction substantially perpendicular to the direction of the wires 56 and out through the perforated bottom 42 into the drying chamber. By having the air flow in this manner, each of the wire elements is contacted by air of substantially the same temperature so that the desired cooling is obtained throughout the heating element to eliminate the occurrence of any hot spots thereon. Such cooling enables the use of wires of alloys such as iron base alloys to operate at a lower heating temperature and therefore enables the construction of the heating unit 53 using a material which is more economical and available than used in prior heating elements which are typically nickel based wire alloys. Since the two insulators 54 and 55 are mounted with a means biasing them apart to mantain the desired tension on the wire element 56, the element can be a straight wire instead of the helically turned wire of the previous heating units and the tensioning prevents sagging or buckling of the wire during a heating operation and eliminates the possibility of shorting between turns or loops due to buckling or sagging of the wire.

An alternate embodiment of the insulator generally indicated at 93 is illustrated in FIGS. 12 and 13. The insulator 93 is provided with fins 94 which are axially spaced along its length to maintain wire loops 95 in spaced relationship to prevent their accidentally contacting or shorting. In between each of the fins 94 the insulator 93 has a passageway 96 to enable a flow of air to cool the insulator. As illustrated in FIG. 13, a portion of each wire loop 95 overlies the passageway 96 to receive the effect of the cooling air. In the design of the insulator 93, only a small portion 98 of each wire loop 95 is in contact with the solid portion of the insulator 93. Thus, the wire loops 95 receive additional cooling to prevent the creation of hot spots thereon during a heating operation.

Each of the embodiments such as the units 15, 15a and 15b are provided with a tab for acting with a coacting slot on the flange 25 of the opening in the bulkhead 21 and the retainer means 50. Thus the unit or heater box assembly 15, 15a or 15b can be easily assembled onto the bulkhead 21 of the dryer device 16. The present structure of the unit not only simplifies the manufacturing of the heating elements 53 and its assembly into the box formed by the members 30 and 31, but also simplifies the installation of the heating box assembly 15 onto the bulkhead 21 whether during initial installation or in a subsequent removal and installation of repair parts.

Although minor modifications might be suggested by those skilled in the art, it should be understood that I wish to embody within the scope of the patent warranted hereon all such modifications as reasonably and properly come within the scope of my contribution to the art.

I claim as my invention:

1. A box for attachment in an opening in a stationary wall of a laundry appliance, the opening having a peripheral flange extending substantially at a right angle to the plane of the wall, comprising:

means for forming a box including one member having a cup-shape portion with a peripheral wall and a perforated bottom, said cup-shaped portion being complementary to the opening and having a size for enabling a snug fit in the opening with the peripheral wall of the portion being engaged with the peripheral flange; and

securing means for attaching the box on the wall with said cup-shaped portion received in the opening including retaining means disposed on said box for attaching the box to the wall and a coacting tab and slot, said coacting tab and slot comprising a tab formed in the peripheral wall of said portion and said slot being formed in the peripheral flange of the opening and being dimensioned to receive said tab so that securing of the box to the wall is accomplished by engaging the coacting tab and slot and preventing their disengagement by completing the securing with the retaining means.

2. A box for attachment in an opening in a stationary wall of a laundry appliance, comprising:

means for forming a box including one member having a cup-shaped portion with a peripheral wall and a bottom, said portion being complementary to the opening and having a size for enabling a snug fit of the peripheral wall of the portion in the opening; and

securing means for attaching the box on the wall with said portion received in the opening, said securing means including a tab coacting with a slit adjacent the periphery of the opening for holding the portion in the opening, and retainer means disposed on said box for attaching the box to the wall, said retainer means comprises strap attached to a side wall of the box furthest removed from said coacting tab and slot, and a fastening means for securing a portion of said strap to the wall of the laundry device, so that securing of the box to the wall is accomplished by engaging the coacting tab and slot and preventing their disengagement by completing the securing with the retaining means. 

1. A box for attachment in an opening in a stationary wall of a laundry appliance, the opening having a peripheral flange extending substantially at a right angle to the plane of the wall, comprising: means for forming a box including one member having a cup-shape portion with a peripheral wall and a perforated bottom, said cup-shaped portion being complementary to the opening and having a size for enabling a snug fit in the opening with the peripheral wall of the portion being engaged with the peripheral flange; and securing means for attaching the box on the wall with said cupshaped portion received in the opening including retaining means disposed on said box for attaching the box to the wall and a coacting tab and slot, said coacting tab and slot comprising a tab formed in the peripheral wall of said portion and said slot being formed in the peripheral flange of the opening and being dimensioned to receive said tab so that securing of the box to the wall is accomplished by engaging the coacting tab and slot and preventing their disengagement by completing the securing with the retaining means.
 2. A box for attachment in an opening in a stationary wall of a laundry appliance, comprising: means for forming a box including one member having a cup-shaped portion with a peripheral wall and a bottom, said portion being complementary to the opening and having a size for enabling a snug fit of the peripheral wall of the portion in the opening; and securing means for attaching the box on the wall with said portion received in the opening, said securing means including a tab coacting with a slit adjacent the periphery of the opening for holding the portion in the opening, and retainer means disposed on said box for attaching the box to the wall, said retainer means comprises strap attached to a side wall of the box furthest removed from said coacting tab and slot, and a fastening means for securing a portion of said strap to the wall of the laundry device, so that securing of the box to the wall is accomplished by engaging the coacting tab and slot and preventing their disengagement by completing the securing with the retaining means. 